Fabrication of Multi-Functional Sintered Materials with Graded Compositional Distribution

对前两年制定的设计方案制作的金属和陶瓷梯度试件进行了激光差温加热试验和氢氧燃烧器火焰加热试验。用声发射监测了试件在加热和冷却过程中的裂纹形成情况。在试验的冷却循环过程中观察到了垂直裂纹的形成。垂直裂纹通过进一步的加热和冷却扩展，最终结合在一起，导致陶瓷层从试件表面剥落。利用测得的温度分布对试件的应力状态进行了有限元分析，结果表明，在加热过程中，陶瓷表面产生了较大的压应力，导致陶瓷层的非弹性变形。在冷却过程中会产生非弹性变形，导致拉应力超过陶瓷的固有强度，导致垂直裂纹的形成。从金属和陶瓷相组成的复合结构中裂纹扩展的微观结构观察发现，提高陶瓷富集区的延性对于保持这类功能梯度材料的热阻是必不可少的。这样的改进将通过通过工艺优化控制富陶瓷区域中的金属相的连接性来实现。隔热性能是通过材料的热阻来评价的，它的值与垂直裂纹形成的加热温度一起，是功能梯度材料热机械性能的特征参数。梯度材料的微观结构控制的概念，特别是关于所涉及的相的连通性的概念，将被应用于其他类型的功能梯度材料，例如

A laser beam differential temperature heating test and a hydrogen/oxygen burner flame heating test were made on the graded specimens of metal and ceramics, fabricated under the design scheme established in the forgoing two years. An acoustic emission monitoring was used to detect the crack formation in the specimen during heating and cooling cycle. Vertical cracks were observed to be formed during cooling cycle of testings. The vertical cracks propagated by further heating and cooling, and they eventually coalesce to result in the spallation of the ceramic layr from specimen surface. Finite element analysis on the stress state in the specimen was done using the measured temperature distribution, and it has shown that a large compressive stress is generated during heating period at the ceramic surface to cause non-elastic deformation of the ceramic layr. The non-elastic deformation will cause during cooling peiod tensile stress, which will exceed the intrinsic strength of the ceramics and result in the formation of the vertical cracks. From the microstructural observations of the crack propagation in the composite structures consisted of metal and ceramic phase the improvement of the ductility of the ceramic-rich regions has been found to be indispensible for the retention of the heat resisrtance of this kind of functionally gradient materials. Such an improvement will be realized by an control of the connectivity of the metal phase in the ceramic-rich region through a process optimization. The heat insulating performance is evaluated by thermal resistance of the material, and its value is a characteristic parameter, along with the heating temperature of the vertical crack formation, for the thermomechanical performance of functionally gradient materials. The concept of the microstructual control of graded materials, particulary with respect to the connectivity of the phases involved, will be applied to the other kind of functionally gradient materials, such as ther